Why are the space crafts and probes we send out, so slow? Why can't we refuel in orbit and lift off again? And get going?
Why so Slow?
- Thread starter Classical Motion
- Start date
When a rocket aims a spacecraft at the edge of the Solar System it burns until it runs out of fuel. If you had a gas station located at that point, you would have to accelerate the gasoline to the same speed as the rocket. So why not just bring it along on the rocket in the first place? There is no savings. Spacecraft on a one way trip out, cannot be refueled.
the rocket can travel half the range,
and brake to re-fuel at the fuel parcel
-or something like that to brake.
The fuel parcel can be grabbed at speed
-if we can mechanically figure something out
and brake to re-fuel at the fuel parcel
-or something like that to brake.
The fuel parcel can be grabbed at speed
-if we can mechanically figure something out
We have tankers for extended sailing. We have tankers for extended flying. Most of space travel will be extended. We will need fuel and supply caches.
But the problem is velocity. We need much faster velocities for human solar system exploration.
It takes way too long just to go to Mars. The closest planet. Along with that V, we will need gravity and shielding.
Gravity and shielding are not developed yet, but we can send the caches on their way. The slow poke way.
Other than fuel, is there any other engineering limits on our craft's velocities? And if not, why are all our crafts so slow?
Can't we stored caches in foreign orbits......and use those orbits for mating up the velocities? Can't we use an orbit for deceleration?
Shouldn't we be learning to do these things? What velocity could we reach, with a fully load rocket in orbit at velocity? Isn't Parker going at a good clip? Can we do the same, without months of gravity acceleration?
But the problem is velocity. We need much faster velocities for human solar system exploration.
It takes way too long just to go to Mars. The closest planet. Along with that V, we will need gravity and shielding.
Gravity and shielding are not developed yet, but we can send the caches on their way. The slow poke way.
Other than fuel, is there any other engineering limits on our craft's velocities? And if not, why are all our crafts so slow?
Can't we stored caches in foreign orbits......and use those orbits for mating up the velocities? Can't we use an orbit for deceleration?
Shouldn't we be learning to do these things? What velocity could we reach, with a fully load rocket in orbit at velocity? Isn't Parker going at a good clip? Can we do the same, without months of gravity acceleration?
There is no way to augment a rocket's fuel once it has reached top speed. We must accept that speed and wait until it reaches its objective. It will zoom by unless there is an atmosphere to slow it down.
If you stop to pick up fuel and then take off and burn it all, you are then going at the same speed you were going before you stopped at the gas station - nothing is gained.
If you station a jug of fuel out there somewhere you cannot just "grab it" as you go by as it would slow you down. Burning it would speed you back up to where you were before the "grab". Nothing gained.
If you put a jug of fuel in an orbit and tried intersecting it, you would be at different speeds. If you gave it a tiny "boost" so it would match up to your space ship it would allow you to refuel. Problem is, you could have done exactly the same thing, using the same amount of fuel by simply attaching that jug to the rocket in the first place.
You can transmit energy to a rocket, microwave beams, lasers, whatever and that energy can be used to expel reaction mass. But there is no way to transmit mass to a moving rocket unless that mass is accelerated to the same velocity.
If you stop to pick up fuel and then take off and burn it all, you are then going at the same speed you were going before you stopped at the gas station - nothing is gained.
If you station a jug of fuel out there somewhere you cannot just "grab it" as you go by as it would slow you down. Burning it would speed you back up to where you were before the "grab". Nothing gained.
If you put a jug of fuel in an orbit and tried intersecting it, you would be at different speeds. If you gave it a tiny "boost" so it would match up to your space ship it would allow you to refuel. Problem is, you could have done exactly the same thing, using the same amount of fuel by simply attaching that jug to the rocket in the first place.
You can transmit energy to a rocket, microwave beams, lasers, whatever and that energy can be used to expel reaction mass. But there is no way to transmit mass to a moving rocket unless that mass is accelerated to the same velocity.
OK Bill. Let's pretend. I developed an orbital technique, which allows fuel transfer without loss of V.
Is there anything else, that limits our velocity in space. Engineering wise?
I mean that our vehicles, can go much faster and stay together, is that correct?
And the reasoning of your post is the only prevention to these higher speeds?
Is there anything else, that limits our velocity in space. Engineering wise?
I mean that our vehicles, can go much faster and stay together, is that correct?
And the reasoning of your post is the only prevention to these higher speeds?
The only way you can transfer fuel to a rocket in flight is to get the fuel going just as fast as the rocket. In that case, there is no advantage over sending the fuel along with the rocket in the first place.
If you plan to stop for fuel, then you waste the energy it took to get you going and you waste time by stopping.
If you plan to stop for fuel, then you waste the energy it took to get you going and you waste time by stopping.
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We will use gravity drive ok? Now is there anything else that limits our V?
For instant...what about corrosion? I would think that increased velocity would increase particle collision.
Could this limit our speeds?
And could increased velocity also mean that we would need more shielding protection?
Is there any other limitations?......I don't mean mass gain or such......we will not even come close to that.
Just in reference to the structure and safety of the craft.
Parker just went thru a solar cloud. A first. It was great. It made it......but what if it where going much faster?
And what about the innards.....can they tell if particles entered and got inside?
For instant...what about corrosion? I would think that increased velocity would increase particle collision.
Could this limit our speeds?
And could increased velocity also mean that we would need more shielding protection?
Is there any other limitations?......I don't mean mass gain or such......we will not even come close to that.
Just in reference to the structure and safety of the craft.
Parker just went thru a solar cloud. A first. It was great. It made it......but what if it where going much faster?
And what about the innards.....can they tell if particles entered and got inside?
Our velocity will be limited only by how big we can make a rocket and how small we can make a payload. The bigger that ratio, the faster the payload will end up going.
Out in the space between our galaxy's stars there are about one million atoms per cubic meter. When we smash into them at high speed it will create some heat on the nose cone. Humans might get a spaceship to 0.1 c but this is about the limit for known technologies, including fission and fusion. Only by using antimatter could we go faster but we don't know how to do that. And we proably will never know how to use it, it's just that difficult. Out current rates of production would require longer than the age of the universe to make enough antimatter to fuel a craft. Plus there is demonstrably no way to store it. Hold it in a vacuum equal to interstellar space, cool it to absolute zero and there would still be enough collisions to burn it up before you could use it in a craft.
Out in the space between our galaxy's stars there are about one million atoms per cubic meter. When we smash into them at high speed it will create some heat on the nose cone. Humans might get a spaceship to 0.1 c but this is about the limit for known technologies, including fission and fusion. Only by using antimatter could we go faster but we don't know how to do that. And we proably will never know how to use it, it's just that difficult. Out current rates of production would require longer than the age of the universe to make enough antimatter to fuel a craft. Plus there is demonstrably no way to store it. Hold it in a vacuum equal to interstellar space, cool it to absolute zero and there would still be enough collisions to burn it up before you could use it in a craft.
The rocket equation tells maximum velocity attainable given an exhaust gas velocity, launch mass and payload mass.
V final = (V of exhaust gas) x (natural log of the ratio of mass at launch divided by mass of payload)
Say, for example, you have a kerosene/LOX rocket motor with an exhaust gas velocity of 3,000 m/s. You have a 5,000 ton Starship on the pad tipped by many similar stages and a tiny, 10 kg payload on top.
Maximum attainable velocity = (3,000 m/s) x natural log of (5,000,000/10)
This equals 39 km/s.
It is 0.0001 of the speed of light.
To get to 0.1 c we would not be allowed a payload any bigger than ten grams.
Problems with nose cone heating in interstellar space don't become noticeable until about 0.1 c where it is about 100W/m^2. At 0.8c it runs into the megawatts.
Chemical propulsion is off the mark by a factor of 10,000.
Fission propulsion can get us up to about 0.003 c.
Fusion could theoretically get us to 0.007 c.
Antimatter could get us up to about 0.15 c.
V final = (V of exhaust gas) x (natural log of the ratio of mass at launch divided by mass of payload)
Say, for example, you have a kerosene/LOX rocket motor with an exhaust gas velocity of 3,000 m/s. You have a 5,000 ton Starship on the pad tipped by many similar stages and a tiny, 10 kg payload on top.
Maximum attainable velocity = (3,000 m/s) x natural log of (5,000,000/10)
This equals 39 km/s.
It is 0.0001 of the speed of light.
To get to 0.1 c we would not be allowed a payload any bigger than ten grams.
Problems with nose cone heating in interstellar space don't become noticeable until about 0.1 c where it is about 100W/m^2. At 0.8c it runs into the megawatts.
Chemical propulsion is off the mark by a factor of 10,000.
Fission propulsion can get us up to about 0.003 c.
Fusion could theoretically get us to 0.007 c.
Antimatter could get us up to about 0.15 c.
Yes, that's the best Musk can do right now.
Gas velocity = square root of combustion chamber pressure.
You want twice the exit velocity? Then you must up the chamber pressure by a factor of 4.
As you can see, when we get to the limit of strength of materials, we are getting less and less for it. Don't expect any short term advances here.
The other facto r is those walls must handle ever increasing temperatures as the pressure goes up. This weakens the walls. Also, walls are a barrier to heat transfer needed for cooling load, which goes up with temperature.
Gas velocity = square root of combustion chamber pressure.
You want twice the exit velocity? Then you must up the chamber pressure by a factor of 4.
As you can see, when we get to the limit of strength of materials, we are getting less and less for it. Don't expect any short term advances here.
The other facto r is those walls must handle ever increasing temperatures as the pressure goes up. This weakens the walls. Also, walls are a barrier to heat transfer needed for cooling load, which goes up with temperature.
We will only use chemical rockets to get to LEO. Once there, ion thrusters give much better performance. They have far higher exit velocities, maybe 60 km/s, maybe 20 times faster. Then we might get to 0.001 c.
I have found on the net that the fastest a rocket has travelled is:-
the fastest man-made object-
'NASA's Juno' rocket spacecraft
-at 365,000 kmh
3000 m/s would give us 10,800 kmh
Deep Space 1, ion thruster craft travelled at 56,000 kmh
A rocket can go much faster than it's motor exhaust speed. You must multiply its exhaust speed by the natural log of the ratio of the launch mass to the payload mass.
Some of the speeds you are quoting come from slingshot maneuvers around other planets. I am only talking about rocket propulsion.
Some of the speeds you are quoting come from slingshot maneuvers around other planets. I am only talking about rocket propulsion.
I think a rocket pushes on the atmosphere it creates in space,
there is the infinite acceleration under thrust
This was told to me a by a docker diesel fitter
In the atmosphere, it's slowed by the aerodynamic,
but pushes on a speeding atmosphere
there is the infinite acceleration under thrust
This was told to me a by a docker diesel fitter
In the atmosphere, it's slowed by the aerodynamic,
but pushes on a speeding atmosphere
And it’s not that our spacecraft are going slow, as we can see in the discussion thus far. It’s that space beyond Earth and the distances between bodies is just astronomical (pun intended).
It’s really far to anywhere, and even more so to far anywheres.
It’s really far to anywhere, and even more so to far anywheres.
Does that rocket equation apply for all rockets everywhere? Does an air to air missile, a rocket on Mars, and a full rocket launch in an established orbit.......all still use that equation?
Right before lift-off, is the rocket V...zero....or is it set at earth's rotational V?
Right before lift-off, is the rocket V...zero....or is it set at earth's rotational V?
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The rocket exhaust does not push against the air. Air just gets in the way of the plume, reducing its potential velocity.
The velocity of a rocket is a function of the rocket mass, the rate at which mass is expelled and the velocity of that expelled mass.
The velocity of the rocket exhaust is function of the delta P inside the combustion chanber versus outside.
In a vacuum, there is a higher delta P thus a higher plume velocity thus a higher rocket speed.
What does the pushing? It is the ball of hot pressurized gases inside the combustion chamber what does it. The gases push against the top of the combustion chamber thus pushing the rocket into space. The pressure against the bottom of the chamber is absent because there is a big hole there.
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Tsiolkovsky's rocket equation works for all rockets whether in the atmosphere or in a vacuum. There are subtle differences but they are not important.
If launched from Earth's surface, then the velocity of the Earth's surface is added.
Thanks Bill. Let me see if I have this right. The launch mass, payload mass ratio changes are considered and converted to a natural scale change, not a common 10 scale change.
And that natural ratio rate(change), is multiplied by the exhaust velocity common rate, to give payload velocity, a final common rate.
Is that right?
And that natural ratio rate(change), is multiplied by the exhaust velocity common rate, to give payload velocity, a final common rate.
Is that right?
Yes, that is correct. Final velocity equals exhaust velocity times the natural logarithm of the ratio: launch mass divided by payload mass. This is valid for any rocket that carries its fuel with it.
The use of the natural log accounts for a non linear relationship between two factors as we examine various options of payload mass/total mass.
"V" = final rocket velocity in terms of nozzle velocity.
If we sit on the pad with 100% payload, we go nowhere
Ratio = 1:1, V=0
If we have, say, 90 ton rocket and 10 ton payload:
Ratio = 10:1, V=2.3
If we have 99 ton rocket and 1 ton payload:
Ratio = 100:1, V= 4.6
In order to double our performance, we must increase our ratio by a factor of ten. We are not getting very much for our money towards the end.
"V" = final rocket velocity in terms of nozzle velocity.
If we sit on the pad with 100% payload, we go nowhere
Ratio = 1:1, V=0
If we have, say, 90 ton rocket and 10 ton payload:
Ratio = 10:1, V=2.3
If we have 99 ton rocket and 1 ton payload:
Ratio = 100:1, V= 4.6
In order to double our performance, we must increase our ratio by a factor of ten. We are not getting very much for our money towards the end.
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